jorgecarleitao commented on a change in pull request #8662:
URL: https://github.com/apache/arrow/pull/8662#discussion_r523421514
##########
File path: rust/datafusion/tests/sql.rs
##########
@@ -1399,3 +1399,22 @@ async fn query_on_string_dictionary() -> Result<()> {
Ok(())
}
+
+#[tokio::test]
+async fn query_without_from() -> Result<()> {
+ // Test for SELECT <expression> without FROM.
+ // Should evaluate expressions in project position.
+ let mut ctx = ExecutionContext::new();
+
+ let sql = "SELECT 1";
+ let actual = execute(&mut ctx, sql).await;
+ let expected = vec![vec!["1"]];
+ assert_eq!(expected, actual);
+
+ let sql = "SELECT 1+2, 3/4, cos(0)";
+ let actual = execute(&mut ctx, sql).await;
+ let expected = vec![vec!["3", "0", "1"]];
Review comment:
💯
I think that this could even be used to simplify many of our tests for
expressions, as it can be more idiomatic than creating a DataFrame with data
and running a projection against it.
##########
File path: rust/datafusion/src/physical_plan/projection.rs
##########
@@ -114,14 +117,33 @@ impl ExecutionPlan for ProjectionExec {
}
async fn execute(&self, partition: usize) ->
Result<SendableRecordBatchStream> {
+ let input = if
self.input.as_any().downcast_ref::<EmptyExec>().is_some() {
Review comment:
I agree with @alamb : this design does not scale as we end up with `if`
statements scattered around the code.
##########
File path: rust/datafusion/src/physical_plan/projection.rs
##########
@@ -114,14 +117,33 @@ impl ExecutionPlan for ProjectionExec {
}
async fn execute(&self, partition: usize) ->
Result<SendableRecordBatchStream> {
+ let input = if
self.input.as_any().downcast_ref::<EmptyExec>().is_some() {
+ placeholder_stream(self.schema.clone())?
+ } else {
+ self.input.execute(partition).await?
+ };
+
Ok(Box::pin(ProjectionStream {
schema: self.schema.clone(),
expr: self.expr.iter().map(|x| x.0.clone()).collect(),
- input: self.input.execute(partition).await?,
+ input,
}))
}
}
+// Makes a stream only contains one null element
+fn placeholder_stream(schema: Arc<Schema>) ->
Result<SendableRecordBatchStream> {
Review comment:
I agree: ingenious 💯
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